The processing of semiconductors often involves multiple process steps such as the deposit of a film on a substrate or substrate by chemical vapor deposition (CVD), the photo etching of the film, as well as heating, cooling and cleaning.
Each of the process operations is generally performed under vacuum in a specialized process chamber. Because of the need for extreme cleanliness and the delicate nature of each process, batch processing of semiconductor substrates has generally been replaced by individual substrate processing. This allows more control of the processing of each substrate, but limits the overall throughput of the system, because, for each process step, the process chamber must be vented, the substrate loaded, the chamber sealed and pumped to vacuum. After processing, the steps are reversed.
To improve the process volume, a cluster of processing chambers are arranged around a substrate transport chamber which is constructed to be kept under vacuum. One or more load lock chambers are connected through slit valves to the transport chamber.
The load locks accommodate cassettes of substrates to be processed. The cassettes are delivered to the load lock by the front end delivery transport of the system. A load lock constructed to accommodate such cassettes is shown in U.S. Pat. No. 5,664,925 owned in common with the subject application. The disclosure of the '925 patent is incorporated herein by reference, in its entirety.
In this manner cycling times are reduced, while significantly increasing system throughput. The process and transport chambers are maintained continuously under vacuum, while only the load lock is cycled. The load lock receives the substrates to be processed after being sealed from the transport chamber and vented to atmosphere. The front end port is than sealed and the load lock is pumped to a vacuum consistent with the transport and processing chambers.
A robotic transfer mechanism is mounted within the transport chamber and operates to remove substrates from the load lock and deliver them to the selected process chambers. After processing, the substrates are picked up by the robot and transported to the next process chamber or to a load lock for removal from the transport chamber. In some instances, for timing purposes, these systems may employ buffer stations which are adapted to store substrates either before loading or at other times during the transport of the substrate through the system.
A system of this type is described in U.S. Pat. No. 5,882,413 and an example of a robotic transfer mechanism is shown in U.S. Pat. No. 5,647,724, each of which is assigned to a owner common to this application. The disclosures of these patents are incorporated herein by reference in their entirety.
It has been found that substrates up to 200 mm in diameter can be effectively processed with the cluster type systems. However, there is a trend towards increasing diameters and the cluster systems become unduly large when processing substrates of 300 mm or more in diameter. There is a need to provide a more compact process handling module, which is capable of being installed in a side by side relation within a small envelope of space. In addition there is a need for system modules which are more adaptable to the wide variety of process chambers and front end delivery transports.
It is a purpose of this invention to provide a load lock chamber which is constructed to service an individual process chamber directly, without a transport chamber and a transport robot. It is a second purpose of this invention to construct a load lock having its own transfer mechanism. It is another purpose of this invention to provide a transport which will accommodate at least two substrates and allow unloading and loading to and from the front end transport during the process cycle.